Strength and ductility of 316L austenitic stainless steel strengthened by nano-scale twin bundles

By means of dynamic plastic deformation (DPD) with high strain rates, a bulk nanostructured 316L austenitic stainless steel consisting of nano-sized grains embedded with bundles of nanometer-thick deformation twins was synthesized. The average transverse grain size is ∼33 nm and the twin/matrix lamellar thickness is ∼20 nm. The nano-twin bundles constitute ∼24% in volume. The nanostructured samples exhibit a high tensile strength of ∼1400 MPa but a limited ductility with a uniform elongation of ∼2%. Subsequent thermal annealing of the as-DPD samples in a temperature range of 730-800 °C led to a single-phased austenite structure consisting of static recrystallized (SRX) micro-sized grains embedded with remaining nano-twin bundles and nano-grains. The annealed DPD samples exhibit an enhanced strength-ductility synergy and much more enhanced work-hardening rates than the as-deformed samples. Work-hardening rates of the annealed DPD samples can be even higher than that of the original CG sample. Tensile ductility was found to increase almost linearly with the volume fraction of SRX grains. A combination of 1.0 GPa tensile strength with an elongation-to-failure of ∼27% is achieved in the annealed DPD 316L stainless steel samples.